Method and apparatus for the continuous regulation of the distance between the electrodes of electrolytic cells with liquid mecury cathodes



Aug. 6, 1968 J. VAN DIEST ETAL 3,396,095

. METHOD AND APPARATUS FOR THE CONTINUOUS REGULATION OF THE DISTANCE BETWEEN THE ELECTRODES .OF ELECTROLYTIC CELLS WITH LIQUID MERCURY CATHODES Filed Dec. 17. 1964 2 Sheets-Sheet 1 V volts Mercury Cell Bot/om mm I ercury "ic ng. b@!! d V I Inifial Position of fhe Anode INVENTORS \IAQUES VAN DIEST JEAN MEN ER g- 1968 J. VAN DIEST ET AL ,396,095

METHOD AND APPARATUS FOR THE CONTINUOUS REGULATION OF THE DISTANCE BETWEEN THE ELECTRODES OF ELECTROLYTIC CELLS WITH LIQUID MERCURY CATHODES Filed Dec. l7, 1964 2 Sheets-Sheet 2 INVENTORS JA QUES VAN wear 3 JEAN MEN/ER United States Patent 9 Claims. (Cl. 204-22s The present invention relates generally to electrolytic mercury cells for the electrolysis of brines and particularly to the control of the distance between electrodes.

The objects of the invention are to improve the control of the distance between the anode and the liquid mercury cathode of electrolytic mercury cells.

An object of the invention is to provide for a setting of the distance between the electrodes while the electrolysis of the cell is continued and electrolysis by the electrode being adjusted is discontinued.

Another object of the invention is to provide for a manual setting of the electrode distances to achieve optimum electrolysis of a solution.

Other objects of the invention are to provide automatic setting of the electrode distances.

The prior art electrolytic mercury cells are disclosed generally in an article by H. A. Sommers in the publication, Chemical Engineering Progress, September 1957, vol. 53, No. 9, pages 409-417. Cells similar to those improved by the present invention are disclosed particularly in Fig. 8 on page 412, in Fig. 9 and Fig. 10 on page 414 and are described on pages 413 to 414 of the Sommers article. In Fig. 8 of the Sommers article a Solvay 170,000 amperes cell is shown installed on two or four levels. In Fig. 9 the Solvay cell-adjustable anode details are given. In Fig. 10 of the Sommers article the Solvay automatic anode adjuster used in the present invention is disclosed.

The prior art manual anode adjustment device of A. Basilewsky is disclosed in US. Patent No. 2,617,762.

The Solvay automatic anode adjuster shown in Fig. 10 of the Sommers article is fully disclosed in US. Patent No. 3,052,618 of Deprez et al.

The prior art anode regulation devices had limitations resulting from the nature of the electrolysis process. Dur ing the electrolysis of brine solutions in electrolytic cells having a mercury cathode the graphite anodes are consumed and the increased distance between the electrode results in a loss of the energy necessary for electrolysis. Due to increased distance between the electrodes it is necessary to regulate from time to time the distance between the anode and the cathode.

In Belgian Patent No. 554,895 a method for regulating the distance between the electrodes without discontinuing the electrolysis process is proposed. While current is being passed continuously between the electrode, the graphite anode is advanced toward the mercury cathode until there is a sudden increase in current. The anode is then retracted until an optimum electrode distance is achieved producing a maximum output for the electrolytic cell. The sudden increase in current can result from a short circuit between the anode to be adjusted and the mercury cathode.

By the procedure of the Belgian patent a geometric point of reference is established such as in the region where there is a definite short circuit. From this geometric point the adjustment can be made. The electrolysis continues during the adjustment of the electrode since the other rows of anodes in the cell remain under voltage, i.e. in operation. The anode being adjusted is surrounded "ice I by a layer of chlorine and a short circuit can occur only when this layer of chlorine disappears. As a result the depth of immersion of the anode in the mercury cathode to obtain a definite short circuit depends on the variables of current density and on the form and degree of erosion of the graphite anode.

The present invention is a definite improvement of the prior art where the distance between the electrodes is regulated independently of the charge on the cell. The result is that the reference point from which the adjustment is made is always the same no matter what the charge on the cell may be. Another new and unexpected result is that the reference point is practically independent of the degree of erosion of the anode.

The invention can best be described by a reference to the drawings.

In the drawings:

FIG. 1 shows a plot of the voltage change in the present invention as the anode is advanced toward the mercury cathode.

FIG. 2 is a schematic representation of the cross-section of a series of Solvay mercury electrolytic cells connected in series with the improvements of the present invention added thereto.

With reference to FIG. 2 the procedure of the present invention is carried out by first opening switch 7 connecting the bottom of the preceding cell 12 with the anodes 25 and 25. Anode 25' represents the anode to be regulated. Since anode 25 and cathode 23 are no longer under a voltage and instrument 29 representing a voltmeter, ammeter or galvanometer can then be connected between the anode 25 and the cathode 23. The apparatus 31 represents the automatic regulation device of U.S. Patent No. 3,052,618 which automatically advances the anode until the voltage suddenly drops and then retracts the anode to a position where the distance between the anode and cathode produces a maximum production of the cell.

FIG. 1 illustrates the voltage variation on galvanometric relay 29 as anode 25' advances toward mercury cathode 23. As the graphite anode contacts the mercury cathode the voltage falls off to zero.

The present invention may be carried out by manually disengaging switch 7 and connecting in series anode 25', the galvanometric relay 29, the capacitor 30 and mercury cathode 23. When the circuit is completed, the galvanometric relay 29 registers a voltage variation. As the anode 25' is advanced toward the cathode, the galvanometric relay 29 registers a fall-off of voltage to zero as the anode contacts the cathode. The control apparatus 31 may be actuated automatically by galvanometric relay 29 to ad vance the anode 25 until it comes in contact with the cathode 23 and then to retract the anode 25' to the optimum electrode position.

In a normal electrolysis operation the cells of FIG. 2 are connected in series. Direct current flows from 34 to copper conductors 6 to the anodes 5 and 5'. Brine solution 4 in cell 1 is electrolyzed by the passage of current from anode plates 8 and 8' to the mercury cathode 3. The current is conducted through the bottom of the mercury cell 2 to copper conductors 6 to the succeeding cell through switch 7. Anodes 15 and 15' and plates 18 and 18' conduct the current through cell 11 and electrolysis brine solution 14 by passage of current to mercury cathode 13. The bottom of the cell 12 conducts the current through a copper connector 6 to switch 7' which is shown in an open position. During the electrolysis operation switch 7 will be connected as shown in the solid lines of switch 7. The current flows through anodes 25 and 25 and anode plates 28 and 28 in cell 21 through the brine solution 24 to mercury cathode 23. The bottom 3 of the cell 22 conducts the current through copper connector 6 to terminal 33.

Without attempting to advance any theoretical explanation, the inventors believe that the anode which is disconnected by the opening of the switch 7 acts like a chlorine electrode because of a certain amount of chlorine gas adsorbed on the graphite anode. The inventors believe that this chlorine electrode accounts for the voltage between the anode and the cathode when electrolysis is discontinued under this anode. The voltmeter is connected between the adjustable anode 25 and the liquid mercury cathode 23 to measure the voltage between the anode and cathode and to determine the exact moment when the graphite anode comes in contact with the layer of mercury. When the contact takes place, the voltage suddenly drops.

A galvanometric relay and a capacitor can be connected in series with the anode to be adjusted and its corresponding mercury cathode so that when the switch 7' is opened and the anode is lowered to the mercury cathode, the capacitor will be charged. At the moment when the graphite anode comes into contact with the mercury cathode, the capacitor discharges suddenly. This method is specially advantageous because it permits the distance between the electrodes to be regulated before the cell is in operation, i.e. it is not under any voltage and there is no sodium in the mercury. It is therefore possible to connect an auxiliary source of current and a resistor between the anode to be adjusted and the mercury cathode in such a manner as to charge the capacitor.

It is obvious that the improvement of the present invention facilitates automatic regulation. The necessary impulse to actuate an automatic anode advancing and positioning mechanism is achieved by the sudden variation of voltage and/or current. For example, when the circuit formed by the capacitor and the galvanometric relay is connected between the anode and the cathode, the relay pointer will swing in a definite direction and will come into contact with a point which is electrically connected with an auxiliary circuit serving to lower the anode, and then return immediately to its original position at the moment when the anode comes into contact with the mercury cathode. The capacitor will discharge and the cessation of electric current will cause the pointer to swing in the opposite direction to that previously observed when the capacitor relay circuit was connected. The pointer will now come into contact with a point connected electrically with an auxiliary circuit for withdrawing the anode to the point where the yield of the cell will be a maximum.

The improved control of the present invention makes it possible to obtain a reference position that is reproducible independently of the charge of the cell and of the degree of erosion of the electrodes.

A further advantage of the present invention is that all the anodes of the cell will be brought to approximately the same optimum distance from the surface of the mercury cathode.

From the foregoing description, one skilled in the art can easily ascertain the esential characteristics of this invention, and without departing from the spirit and scope thereof can make various changes and modifications of the invention to adapt it to various usages and conditions. Consequently, such changes and modifications are properly, equitably, and intended to be, within the full range of equivalence of the following claims.

What is claimed is:

1. A method for the continuous regulation of the distance between the anode and mercury cathode of electrolytic mercury cells used in the electrolysis of brine, each of said mercury cells having switching means and circuit means connecting the cathode of each mercury cell with the anode of the next mercury cell, the steps comprising:

(a) disconnecting said switching means to discontinue the electrolysis;

(b) connecting measuring instrument means in series with the anode to be regulated and the mercury cathode with which said anode cooperates to produce an electrolysis;

(c) advancing said anode to be regulated toward said mercury cathode;

(d) halting the advance of said anode when said measuring instrument means adapted to indicate voltage and current indicates a sudden decrease; and

(e) retracting said anode from a point in space at which it was halted a predetermined distance said distance being chosen for producing optimum conditions for maximum electrolysis production.

2. The method of claim 1 wherein said measuring instrument of (b) actuates said advancing (c), halting (d) and retracting (e).

3. The method of claim 1 wherein said measuring instrument means is a voltmeter.

4. The method of claim 1 wherein said measuring instrument means is an ammeter.

5. A method for the continuous regulation of the distance between the anode and mercury cathode of electrolytic mercury cells used in the electrolysis of brine, each of mercury cells having switching means and circuit means connecting the cathode of each mercury cell with the anode of the next mercury cell, the steps comprising:

(a) disconnecting said switching means to discontinue the electrolysis;

(b) connecting a galvanometer and a capacitor in series with the anode to be regulated and the mercury cathode with which said anode cooperates to produce an electrolysis;

(c) advancing said anode to be regulated toward said mercury cathode;

(d) reversing the advance of said anode when said galvanometer indicates a sudden decrease and said anode contacts said mercury cathode; and

(e) retracting said anode from a point in space at which reversal was begun a predetermined distance, said distance being chosen for producing optimum conditions for maximum electrolysis production.

6. In an electrolytic mercury cell for the electrolysis of brines having at least one adjustable anode, a mercury cathode and a direct current source connected in series, the improvement comprising:

(a) switching means connected in series with said mercury cathode, said adjustable anode and said current source discontinuing electrolysis of said mercury cell;

(b) means for advancing said adjustable anode and for retracting said adjustable anode a predetermined distance; and

(c) measuring instrument means connected in series with said adjustable anode and said mercury cathode and the advance of said adjustable anode is reversed when said measuring instrument indicates a sudden decrease and said adjustable anode is retracted a predetermined distance from a point of reversal in space, said distance being chosen for pro ducing optimum conditions for maximum electrolysis production.

7. In an electrolytic mercury cell for the electrolysis of brines having at least one adjustable anode, a mercury cathode and a direct current source connected in series, the improvement comprising:

(a) switching means connected in series with said mercury cathode, said adjustable anode and said current source whereby electrolysis of said mercury cell is discontinued;

(b) means for advancing said adjustable anode and for retracting said adjustable anode a predetermined distance after advancement;

(c) measuring instrument means connected in series with said adjustable anode and with said mercury cathode said measuring instrument being connected to indicate a sudden decrease upon contact between said adjustable anode and said mercury cathode; and

(d) circuit means connecting said instrument means with said advancing and retracting means and said instrument means actuates said advancing and retracting means.

8. In an electrolytic mercury cell for the electrolysis of brines having at least one adjustable anode, a mercury cathode and a direct current source connected in series, the improvement comprising:

(a) switching means connected in series with said mercury cathode, said adjustable anode and said current source for discontinuing electrolysis of said mercury cell;

(b) means for advancing said adjustable anode and for retracting said adjustable anode a predetermined distance upon cessation of advancement; and

(c) means comprising galvanometric means and a capacitor connected in series with said adjustable anode and said mercury cathode and means whereby the advance of said adjustable anode is reversed when said galvanometric means indicates a sudden decrease and said adjustable anode is retracted a predetermined distance upon ceasing its advance, and said distance producing optimum conditions for maximum electrolysis production.

9. In an electrolytic mercury cell for the electrolysis of brines having at least one adjustable anode, a mercury cathode and a direct current source connected in series, the improvement comprising:

(a) switching means connected in series with said mercury cathode, said adjustable anode and said current source for discontinuing electrolysis of said mercury cell;

(b) means for advancing said adjustable anode and for retracting said adjustable anode a predetermined distance from a point of commencement of reversal;

(c) galvanometric means and a capacitor connected in series with said adjustable anode and said mercury cathode including means connecting said galvanometric means for indicating a sudden decrease upon contact between said adjustable anode and said mercury cathode; and

(d) circuit means connecting said galvanometric with said advancing and retracting means whereby said galvanometric means actuates said advancing and retracting means.

References Cited UNITED STATES PATENTS 2,328,665 9/1943 Munson 204-250 2,508,523 5/1950 Krebs 204219 XR 2,834,728 5/1958 Gallone 204219 3,052,618 9/1962 Deprez et al 204-219 3,268,427 8/1966 Schiicker 204-99 3,301,776 1/1967 Hughes 204-443 FOREIGN PATENTS 23,309 12/1961 Japan. 554,895 2/1957 Belgium.

JOHN H. MACK, Primary Examiner.

D. R. VALENTINE, Assistant Examiner. 

1. A METHOD FOR THE CONTINUOUS REGULATION OF THE DISTANCE BETWEEN THE ANODE AND MERCURY CATHODE OF ELECTROLYTIC MERCURY CELLS USED IN THE ELECTROLYSIS OF BRINE, EACH OF SAID MERCURY CELLS HAVING SWITCHING MEANS AND CIRCUIT MEANS CONNECTING THE CATHODE OF EACH MERCURY CELL WITH THE ANODE OF THE NEXT MERCURY CELL, THE STEPS COMPRISING: (A) DISCONNECTING SAID SWITCHING MEANS TO DISCONTINUE THE ELECTROLYSIS; (B) CONNECTING MEASURING INSTRUMENT MEANS IN SERIES WITH THE ANODE TO BE REGULATED AND THE MERCURY CATHODE WITH WHICH SAID ANODE COOPERATES TO PRODUCE AN ELECTROLYSIS; (C) ADVANCING SAID ANODE TO BE REGULATED TOWARD SAID MERCURY CATHODE; (D) HALTING THE ADVANCE OF SAID ANODE WHEN SAID MEASURING INSTRUMENT MEANS ADAPTED TO INDICATE VOLTAGE AND CURRENT INDICATES A SUDDEN DECREASE; AND (E) RETRACTING SAID ANODE FROM A POINT IN SPACE AT WHICH IS TWAS HALTED A PREDETERMINED DISTANCE SAID DISTANCE BEING CHOSEN FOR PRODUCUNG OPTIMUM CONDITIONS FOR MAXIMUM ELECTROLYSIS PRODUCTION. 